Recently, as part of the measure against global warming, various energy conservation measures have been cried out. One of such measures includes use of inverters for power-saving. Various other technologies have also been proposed in association with the trend. For example, in Japanese Patent Application Laid-Open Publication No. 2001-155083, discloses a technology that provides, in a facility that is subject to measurement of its power consumption, measuring devices such as ammeters and voltmeters, and a data collecting system that collects and processes the values detected by the measuring devices. Furthermore, power consumption as data corresponding to the volume of air before and after introduction of an inverter is collected, and from that data the data collecting system calculates a difference in the power consumption before and after the introduction of the inverter. In short, in this technology, the difference between the power consumptions when the inverter is used and not used is used to determine the contribution of the inverter to the power saving.
In this technology, to display how much power has been saved, a display device and the like are required to be additionally provided besides both the subject facility and an installed equipment. That is, peripheral equipment for power measurement and a computer for processing data and the like are separately required conventionally besides the inverter in order to display power-saving effects. In addition, a data transmitting unit that transmits the data from the subject facility to the computer is required, which leads to increase in the costs. Furthermore, when it is necessary to intermittently communicate with the computer, there are disadvantages that the sampling of the power consumption becomes rough and an integration error becomes large.
When monitoring the difference between the power consumptions, that is, power-saving effects, it would be significantly convenient if current values and voltage values detected in the inverter itself, precisely, inside the control circuit of the inverter, can be used. It would be further convenient if a central processing unit (CPU) of the inverter can be used for the sampling.
Still further, even when an environmental change and a secular change occur in the inverter or in the subject facility, or even when a load change occurs in the inverter, it is possible to keep a margin of error small if monitoring is carried out according to these changes. However, data at the time of commercial use without the inverter includes values that have been measured in advance, and that includes values of the power consumption corresponding to volume of air. Because a change in current value that can be caused by an environmental change and the like is not considered in the data, a large margin of error occurs in the data with respect to the actual state. Moreover, if, for example, a motor of 22 kilo watts (kW) is used in anticipation of a load of 22 kW, and if a load of 11 kW is actually applied to the motor, the margin of error becomes larger in the data at the time of commercial use as shown in FIG. 5 because inverter control of 11 kW is carried out for the load of 22 kW instead of the load of 11 kW.
Patent Literatures
Japanese Patent Application Laid-Open Publication No. 2001-4677
Japanese Patent Application Laid-Open Publication No, H11-206188
Japanese Patent Application Laid-Open Publication No. 2001-355577
Accordingly, an object of the present invention is to provide a power-saving effect displaying unit in an inverter that carries out monitoring and sampling and that has a reduced error even when an environmental change and a secular change occur in a subject facility, or even when a load change occurs in the inverter.